Method of remoying oxygen from gases



United States Patent Ofifice 3,124,416 Patented Mar. 10, l 964 V 3 124416 METHOD or REMiWliNG OXYGEN rnoM GASES Johann G. E. Colin, WestGrange, and Aifred .l. Haley, In,

Coionia, N..l., assigncrs to Engelhard Industries, inc,

Newark, N..l.-, a corporation of {Deiaware No Drawing. Filed Aug. 12,I960, Ser. No. 49,120

. l Ciaim. (Cl. 23-2) This invention relates to a process for effectingcombustion reactions of oxygen-containing gases and more particularlyrelates to specific fuel-catalyst combinations which afford low ignitionor kindling temperatures of specific fuels in admixture withoxygen-containing gases.

This application is a continuation-in-part of our prior co-pendingapplication Serial No. 650,863, filed April 5, 1957, now abandoned.

Two broad types of applications are of special importance inconnectionwith the catalytic combustion reactions. In the first case, thecatalytic reaction of the fuel and oxygen is conducted with the fuelpresent in an amount stoichiometrically equivalent to or greater thanthe oxygen content. A typical example would be a process in which it wasdesired to remove all of the oxygen from a gas stream and in this case aslight fuel excess would be required. Specifically, for a streamcontaining, by volume, 3.5 percent oxygen and 96.5 percent nitrogen, itwould be necessary to use at least 1 percent by volume of ethane, forexample. In industrial uses, reactions in this category may have theobjective of producing heat as well as removing oxygen. 7

In the second case, the catalytic fuel-oxygen reaction is conducted withthe oxygen present in excess over the fuel, and an example of this typeof process is one in which undesirable hydrocarbons are removed from airstreams. In a specific case in the production of liquid air, it isnecessary to remove small amounts of acetylene from the .air stream inorder to prevent condensation of solid acetylene in cold portions of theequipment result ing in serious explosion hazards.

Another way of differentiating between the two types of processes isthat in one case purification of gas streams from oxygen is theobjective and in the other the objective is to purify gas streams fromhydrocarbons.

In accordance with the present invention, the oxygen of theoxygen-containing gas is reacted with a fuel of the group consisting ofethylene and benzene at an oxygen concentration not in excess of thestoichiometric quantity required for complete reaction with thehydrocarbon I fuel, at an ignition temperature not higher than about 150C. in contact with a palladium metal catalyst. The

reaction is effected by contacting an admixture of the oxygen-containinggas and ethylene or benzene with the catalyst at the temperaturespecified.

Ignition temperatures not higher than about 150 C. are employed in theinstant process utilizing the catalyst specified to avoid unnecessaryand prolonged exposure of the catalyst to high temperatures, which mayresult in detrimental effects to the catalyst and impairment of itscatalytic activity. The reaction of the oxygen with ethylene or benzeneis an exothermic one and prolonged exposure of the catalyst totemperatures of about 700 C. or higher should be avoided. With thecatalysts of this invention it is possible to provide feed to thecatalysts at a lower ignition temperature than heretofore known, so thatfor a given mixture of oxygen-containing gas and fuel with a given AT ofreaction the final reaction temperature is lower. It is also possible inaccordance with this invention to supply a larger amount of the minoringredient of the reaction (and thus react a greater amount of suchingredient with the result of a higher AT) without heating the catalystto the extent of damaging it.

The catalyst may be supported on suitable supports For optimumconversion, the catalyst should be present within the range of about0.1-2 percent or more by weight of the catalyst metal and support andthe catalyst may be in the form of pellets, granules, or powder andpreferably comprises activated alumina. The supported catalyst may beprepared in any suitable manner, i.e. by treating the carrier or supportwith a solution of a suitable metal compound and then reducing the metalcompound to metal.

The fuel for which the palladium catalyst has been found to beefiicacious in burning at a low ignition temperature is one from thegroup consisting of ethylene or benzene, and this fuel may contain watervapor up to 5 volume present, or more. At water vapor concentrationsabout 2 percent by volume, there is in some cases a slight increase inthe temperature required for ignition.

The space velocity may be in the range of about 10,000 to 200,000standard volumes of gas per volume of catalyst per hour, and a spacevelocity in the range of about 50,000 to 200,000 standard volumes pervolume per hour is of industrial importance. The pressure may be in therange of atmospheric to about 500 p.s.i.g. or higher. The process may beconducted in two stages if desired, with intermediate cooling betweenstages in a manner similar to that disclosed in co-pending applicationSerial No. 650,860, filed April 5, 1957, now Patent No. 2,970,034.

Examples of oxygen-containing gases or gas which can be reacted with thehydrocarbon fuel in accordance with the invention include atmosphericair, mixtures of oxygen and nitrogen, e.g. mixture containing, byvolume, 3.5 percent oxygen and 96.5 percent nitrogen, oxygen-enrichedair, and waste gases containing oxygen and oxides of nitrogen from theammonia oxidation process. 7

The invention will be further illustrated by reference to the followingspecific example.

EXAMPLE I A series of runs was made to study the effectiveness ofvarious specific catalysts with separate ethylene and benzene fuels, andthe procedure consisted of passing a mixture of the ethylene or benzenefuel and an oxygennitrogen mixture over the catalyst to be evaluated.During the period of gas flow, the temperature of the catalyst wasgradually raised and for each catalyst the temperature was determined atwhich it began to promote combustion. Once this ignition point wasreached, the heat liberated by the combustion reaction raised thetemperature of the gas, and the final temperature is the result of theheat of the combustion, the heat capacity of the gaseous products aftercombustion, and the heat losses in the reactor system. For the purposeof the present invention, only the ignition temperature is of interestand this temperature may also be termed the kindling or takeofftemperature.

In Table I are listed the ignition temperatures for various combinationsof ethylene or benzene fuel, oxygencontaining gases, and catalysts, andthese ignition temperatures are to some extent a function of the reactorsystem employed, i.e. with the relatively low gas flows em ployed therewas a considerable heat loss effect which would not be observed withlarge gas flows. Generally, the ignition temperatures observed underconditions of large gas flows under essentially adiabatic conditions arelower than those shown in the table. However, this effect does not alterthe relative scale of catalyst activity shown in the table.

In Table I below, two sets of ignition temperatures are listed for eachhydrocarbon, A being the ignition tem- 3 perature of a mixturecontaining3 percent oxygen by volume and a stoichiometrically equivalent amount ofhydrocarbon with the balance being nitrogen, and B being the ignitiontemperature of a mixture of air and hydrocarbon equivalent to 3 percentby volume of oxygen. The A condition is one in which the oxygen andhydrocarbon are in exact balance, i.e. the atmosphere surrounding thecatalyst is neutral insofar as oxidation is concerned, While the Bcondition is for a gaseous mixture in which the oxygen is present in aconcentration seven times as great as the hydrocarbon. This distinctionis of considerable importance in different applications of thisinvention to the treatment of specific gas streams.

The results are as follows:

Table l gen from a gas mixture consisting essentially of primarilyelemental nitrogen and also a small amount of the oxygen of the order ofabout 3%, which comprises admixing a material selected from the groupconsisting of ethylene and benzene as fuel with said gas mixture, thefuel being present in the resulting admixture in amount of from thatstoichiometrically equivalent to the oxygen content to a slight excessover the stoichiometric equivalent, and passing the resulting gaseousadmixture into contact with a palladium metal catalyst at an ignitiontemperature of said admixture within the range of 140 C. to about 150 C.thereby reacting the fuel with the elemental oxygen to remove the oxygenfrom the admixture.

IGNITION TEMPERATURES OF HYDROCARBON-OXYGEN-NITROGEN MIXTURES OVERVARIOUS CATALYSTS [Total flow rate= it. per hr. at 1 atmosphere pressureusing 2.5 gm. catalyst. T Q.=Minimum temperature required to sustainreaction. Catalyst support=%" activated alumina pellets] A B A BCatalyst Ignition tempera- Ignition temperature of mixture Ignitiontemperature of mixture Ignition temperaeontaining 3% O ture of mixturecontaining 3% O ture of mixture stoichiometric of air andhydrostoichiometric of air and hydroequivalent of carbon equivalentequivalent of carbon equivalent hydrocarbon, to 3% oxygen, C.hydrocarbon, to 3% oxygen, 0. balance nitrogen, balance nitrogen, 0. C.

0.5% Pt on A1 03 160 200 0.5% Pd on A1 03. 150 230 210 0.5% Ru on AlzO3.5 240 270 335 0.5% Rh on Alg03 300 312 275 320 0.5% Ag on A10 500 Fromthe above table it will be seen that where ethylene is used as the fuel,the best catalyst for the A condition is palladium on alumina, Palladiumon alumina is also the best catalyst for the A condition when benzene isused as fuel.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

A process for effecting the removal of elemental oxy- References Citedin the file of this patent UNITED STATES PATENTS 644,160 Boehn Feb. 27,1900 2,351,167 Ware June 13, 1944 2,579,620 Smith Dec. 25, 19512,973,384 Hayashi et a1. Feb. 28, 1961 FOREIGN PATENTS 436,906 GreatBritain Oct. 21, 1935 565,991 Great Britain Dec. 7, 1944

